A commercially successful integrated circuit (IC) is often dependent upon high product yields to keep manufacturing costs at a level that provides product profitability at market competitive prices. The phrase “product yield,” in terms of ICs, is typically defined as the percentage of functional ICs generated out of the total number of ICs fabricated using a particular manufacturing process for ICs. IC product yield is affected by a variety of factors that permeate nearly the entire manufacturing process.
One cause of decreased IC product yield relates to process imperfections. Process imperfections can create parameter variations between process runs for an IC, between differing wafers within a single process run, or between ICs within a same wafer. For example, the value of a particular resistor can vary from one IC to another according to the geographic region of the wafer in which each IC is located. In another example, capacitance values may be higher on wafers processed at the beginning of a process run than wafers processed at the end of the process run.
Another cause of decreased IC product yield relates to the testing equipment itself. More particularly, test and/or measuring equipment can lose calibration or alignment resulting in the collection of inaccurate data. Assessing inaccurate data can lead to the rejection of operable ICs and, therefore, the needless degradation of product yields.